Polymeric roof sheeting is used as single ply roofing membrane for covering industrial and commercial flat roofs. Such membranes are generally applied to the roof surface in vulcanized or cured state.
Because of outstanding weathering resistance and flexibility, cured elastomeric roof sheeting has been rapidly gaining acceptance. This material normally is prepared by vulcanizing the composition in the presence of sulfur or sulfur containing compounds such as mercaptans. Our earlier U.S. Pat. No. 4,803,020 also teaches the use of radiation crosslinking promoters in an EPDM sheeting composition which can be cured by ionizing radiation. Vulcanization and curing can be done in the presence of other compounds as well. For example, ethylene-butene copolymers may be cured in the presence of triazine or organic peroxide.
Notwithstanding the usefulness of radiation curing, sulfur curing, and triazine curing, a disadvantage of utilizing these elastomers is the lack of adhesion of these elastomers, especially cured olefinic elastomers to themselves. This is a serious problem because in applying elastomeric sheets to a roof, it is usually necessary to splice the cured elastomeric sheets together. This splice or seam area is subjected to both short term and long term stresses such as those caused by roof movement, heavy winds, freeze-thaw cycling and thermal cycling. Such stresses may manifest themselves in shear forces or peel forces, i.e., the seam peels back under severe stress conditions or results in a partially open seam (often referred to as a fish-mouth condition) under less severe conditions.
In view of the foregoing problem, it has been necessary to utilize an adhesive to bond the cured elastomeric sheets together. As will be evident from the above discussion, an adhesive for bonding cured elastomeric roofing sheets together must meet a number of requirements which are extremely difficult to satisfy. Thus, the adhesive must provide sufficient peel and adhesive strength to permit the splice formed by bonding the cured elastomeric roofing sheets together to resist both the short term and long term stresses such as those discussed hereinabove. Moreover, the adhesive must be resistant to oxidation, hydrolysis and chemical attack from portred water. Additionally, the adhesive must provide the important property often referred to in the adhesive art as "Quick Stick". The term "Quick Stick" means the characteristics of two sheets of material which have been coated with an adhesive composition to develop virtually immediate adhesive strength when placed in contact with each other.
Quick Stick is an extremely important property in an adhesive which is utilized to splice cured elastomeric roofing sheets together. Thus, adhesive compositions presently known generally require anywhere from about two (2) to about seven (7) days at room temperature (i.e. 22.degree. C.) to attain maximum adhesive strength. At higher ambient temperature, this time period may be somewhat less but at minimum it will generally be at least 24 hours. The conventional procedure for splicing the elastomeric roofing sheets together is to make the splice within a relatively short period of time after the adhesive coating has been applied to each sheet, generally within 30 minutes but often less. Accordingly, the adhesive composition must provide sufficient immediate adhesive strength or Quick Stick to permit the splice to withstand stresses from winds, movement, handling by installers, etc. until the adhesive achieves its maximum strength which as indicated will generally take from two (2) to seven (7) days.
Commercial contact adhesives which are conventionally employed for bonding cured elastomeric roofing sheets together generally consist of solutions of neoprene or neoprene-type or butyl or butyl-type polymers in aromatic or aromatic-aliphatic solvents containing 2-butanone often along with tackifying resins. However, such adhesives have not proven to be very satisfactory due to their lower than desirable peel adhesion strengths. Thus, the neoprene or butyl-type adhesives often provide peel adhesion values at 22.degree. C. of only 1 to 2 pounds per linear inch.
Pressure sensitive and contact adhesive compositions containing neutralized, partially neutralized or unneutralized sulfonate elastomers, tackifying resins and organic solvents or organic solvent mixtures are known in the prior art as shown by U.S. Pat. Nos. 3,801,531 and 3,867,247.
U.S. Pat. No. 3,801,531 relates to pressure sensitive adhesive compositions which contain thiouronium derivatives of unsaturated elastomers or neutralized, partially neutralized or unneutralized sulfonated elastomers including sulfonated EPDM, tackifying resins including phenol formaldehyde or alkylphenol formaldehyde resins and organic solvents or organic solvent mixtures including a preferred 90:10 mixture of toluene and isopropyl alcohol. However, the patent does not disclose or suggest the use of alkylphenols or ethoxylated alkylphenols in such compositions.
U.S. Pat. No. 3,867,247 relates to adhesive contact cements which contain neutralized, partially neutralized or unneutralized sulfonated butyl elastomers, tackifying resins including phenol formaldehyde or alkylphenol formaldehyde resins and organic solvents or organic solvent mixtures including a preferred 90:10 mixture of toluene and isopropyl alcohol. However, the patent does not disclose or suggest the use of alkylphenols or ethoxylated alkylphenols in such compositions.
The adhesive compositions described in the aforementioned patents suffer from a significant disadvantage which materially limits their usefulness as a contact adhesive for bonding cured elastomeric roofing sheets together and that is their deficiency in Quick Stick properties.
One such adhesive system for olefinic elastomers that provides good Quick Stick is described in U.S. Pat. No. 4,480,012, owned by the Assignee of record herein. Such adhesives comprise a neutralized sulfonated EPDM elastomeric terpolymer; an organic hydrocarbon solvent; a para-alkylated phenol formaldehyde tackifying resin and an alkylphenol or ethoxylated alkylphenol.
Notwithstanding the problem of adhesion, the elastomeric roof sheeting materials also lack flame resistivity. In order to improve the flame resistivity of the product using the olefinic elastomers, fillers such as antimony trioxide, decabromo diphenyl oxide (DBDPO), dechlorane (chlorinated alicyclic hydrocarbon) alumina trihydrate, and chlorinated or brominated paraffins, are normally incorporated into the composition as shown in U.S. Pat. Nos. 4,839,412 and 4,851,463. However, the capacity of these membranes to accept these flame retardant fillers is somewhat limited, especially with membranes which exhibit thermoplastic characteristics.
Furthermore, U.S. Pat. No. 4,801,639 relates to flame retardant olefinic resin compositions which comprise a mixed resin of olefin and a silane-grafted polymer, a hydrated metal compound and a dicarboxylic acid or dicarboxylic acid anhydride derivative.
Therefore, while the use of adhesive compositions and flame retardant additives are effective means of joining and sealing the edges of elastomeric roofing material and increasing flame retardancy, respectively, if the use of adhesives could be eliminated and/or the amount of flame retardant additive reduced, the additional labor and material costs and related hardware necessary to apply the adhesive or incorporate the additive would effect a significant cost savings. Moreover, elimination of the need to cure the material prior to its application to a roof would also be advantageous. Also, a need for elastomeric roofing material with improved seam strength at elevated temperatures and improved flame retardancy continues to exist.